February was generally warmer and sunnier than January (14% less heating degree days, 38% more sun), not to mention 2 days shorter. This partially resulted in 24% lower energy usage in February. (I say, ‘partially resulted’ because we don’t have heating energy values separated out from the total load yet.) If you look at it from a daily usage perspective we’re down 18% from January. That almost got us close to netting out to zero for February.

  1. January values based on meter reads.
  2. February values based on TED data.
  3. Heating Degree Days (a measure of how many outside degrees in a day it is below a target inside temperature)
  4. Downloaded from degreedays.net, Station ID: KALB (Albany International Airport).
  5. Calculated from my HOBO outdoor weather monitor hourly data.
All values in kWh (except HDD) Jan 2012 1 Feb 2012 2 Mar 2012
Solar PV generation 369 597 --
Usage 873 666 --
Net usage or (generation) 504 69 --
Average daily usage 28 23 --
HDD (base temp 68F) 3 1,212 4 1,045 5 --

I put together a few charts to compare a cloudy day where the temperatures are dropping throughout the day (February 2nd), and a relatively sunny day where the temperature is rising (February 3rd). There’s always a spike in the morning, the heat, hot water, water pump, and coffee maker all generally go on around the same time. But you can see in this first chart that the HDD day values are low in the morning, meaning it was fairly warm outside in the upper 30’s. No need for the heat pump to kick in. There’s little green on this chart meaning we were not generating a lot of solar power on this day. It also means the house inside temperatures were not getting much help from the sun. Notice how the HDD is getting bigger as the day progresses. It’s getting colder out, down in the mid 20’s. There is clearly more energy being used in the evening as a result.

Compare with the next day below. It continues to get colder until about 8am when it reaches 18F outside. Notice that the heat pump has popped on a few times in the early morning before the morning rush. Then the sun takes over and the temps start to rise, meaning the HDD values get smaller. Very little energy used after the sun kicks in. Evening power spikes a few times for cooking and cleaning.

There’s no big surprises here, but it is fun to see the correlation in data.

We also generated our 6th megawatt in February. It took roughly 61 days to generate this megawatt.

Megawatt Hour Date Days
0 Jun 2 2011
1 Jul 7 2011 35
2 Aug 8 2011 32
3 Sep 13 2011 36
4 Nov 1 2011 49
5 Dec 29 2011 58
6 Feb 28 2012 61

If you have any questions (or spot any errors), let me know in the comments.